Variable Temperature and Moisture Requirements for Germination within Populations of Kochia (<i>Bassia scoparia</i>) in Field Margins
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Author ORCID Identifiers

Brian Schutte:
https://orcid.org/0000-0003-0356-3565

Rebecca Creamer:
https://orcid.org/0000-0002-5058-2980

Description

Abstract

In areas bordering crop fields in the Southwest United States, extended periods of seedling emergence by kochia [Bassia scoparia (L.) A. J. Scott] complicate management of a pathogenic plant virus (Beet curly top virus (BCTV, Geminiviridae). This is because B. scoparia plants that emerge mid-spring through summer host beet leafhoppers (Neoaliturus tenellus) that vector BCTV. To better understand the causes of, and influences on, prolonged emergence by B. scoparia in marginal environments, we tested the following hypotheses: 1) B. scoparia populations produce subpopulations of seeds that cannot germinate at low temperatures but germinate at high temperatures, and 2) the inhibitory effects of reduced osmotic potential on B. scoparia germination are stronger under a higher temperature. Our study included two growth chamber experiments that were each divided into two sequential phases. Phase 1 subjected seeds to a low temperature treatment (7 °C or 5/10 °C). Phase 2 subjected seeds to either a low temperature (7 °C or 5/10 °C) or high temperature treatment (30 °C or 25/35 °C). A third growth chamber experiment subjected seeds to either 7 °C or 30 °C and determined the proportions of seeds that germinated across a range of temperature-specific osmotic potentials. In the experiments with the two-phase assays, 67% and 73% of B. scoparia seeds germinated at a low temperature (7 °C and 5/10 °C, respectively) during Phase 1. During Phase 2, germination percentages were significantly greater under the high temperature compared to the low temperature. In the osmotic potential experiment, the osmotic potential that reduced B. scoparia germination by 50% was -1.12 MPa at 7 °C, -1.0 MPa at 30 °C. Evidence supporting our hypotheses suggests: 1) B. scoparia seedlings emerging mid-spring through summer originate from seeds with obligate high temperature requirements germination, and 2) late-season soil drying causes greater reductions in B. scoparia germination than early-season soil drying.

 

Methods

The first objective (Objective 1) of this study was to test the hypothesis that Bassia scoparia populations in field margins produce subpopulations of seeds that cannot complete germination at low temperatures and produce seedlings at relatively high temperatures. The second objective (Objective 2) was to test the hypothesis that the inhibitory effects of reduced osmotic potential on B. scoparia germination are stronger under a higher temperature.

To accomplish Objective 1, a laboratory study was conducted to determine temperature requirements for germination. This study involved two types of germination assays. One type of assay subjected seeds to temperatures that did not fluctuate daily (herein, “constant temperature assay”). The other type of assay subjected seeds to temperatures that changed within 24-hour (h) periods (herein, “fluctuating temperature assay”). Each assay type involved two sequential phases and two germination chambers (Model GR41VL; Percival Scientific, Perry, IA, USA). During Phase 1 of the constant temperature assay, both chambers were set to 7 °C. For Phase 2, the temperature in one chamber was changed to 30 °C while the other chamber remained at 7 °C. For the fluctuating temperature assay, both chambers were set to 5/10 °C (10/14 h, respectively) during Phase 1. Phase 2 was initiated by changing one chamber to 25/35 °C (10/14 h, respectively) while the other chamber remained at 5/10 °C. For both constant and fluctuating temperature assays, the duration of each phase was 6 days (d). Interiors of germination chambers were not illuminated during assays, although seeds were not kept in darkness during data collection. Each assay type was repeated. Between experimental runs, with the two temperature treatments [cool followed by (fb) cool, cool fb warm] were rotated between chambers.

Experimental units were plastic containers (4 cm depth, 15 cm width, 15 cm length) with a layer of moistened germination paper and 100 B. scoparia seeds from the same population. Experimental units were arranged on chamber shelves in a randomized complete block design with four replicates. Bassia scoparia seeds were monitored for germination daily. A seed was considered to have completed germination when the radicle broke through the seed coat and elongated at least 2 mm. Once germinated seeds were detected, they were removed from the container. Following Phase 2, seeds that did not complete germination were tested for viability using a 0.6% aqueous solution of 2,3,5-triphenyl-tetrazolium chloride (TZ).

To accomplish Objective 2, the effect of temperature on osmotic inhibition of B. scoparia germination was determined with germination assays that subjected seeds to either 7 °C or 30 °C. An experimental unit was a Petri plate (100 × 15 mm) lined with blotter paper moistened with a polyethylene glycol 6000 (PEG) solution (described below). Each experimental unit contained 30 B. scoparia seeds from the same. PEG solutions were prepared to obtain osmotic potentials equal to 0, -0.25, -0.50, -1.0, and -1.5 MPa at 22.5 °C following procedures in https://doi.org/10.1104/pp.51.5.914. Osmotic potentials were verified using a vapor pressure osmometer. Osmotic potentials of PEG solutions at germination assay temperatures (7 °C and 30 °C) were calculated using an equation that combines ambient temperature and PEG concentration (https://doi.org/10.1104/pp.51.5.914). Accordingly, osmotic potentials of PEG solutions at 7 °C were 0, -0.30, -0.58, -1.11, and -1.65 MPa. At 30 °C, osmotic potentials were 0, -0.22, -0.46, -0.95, and -1.44 MPa.

The duration of each germination assay was 10 d. Seeds were evaluated daily for germination using the criteria described for Objective 1. Upon detection, germinated seeds were removed. At the conclusion of germination assays, seeds that did not complete germination were tested for viability using the TZ solution and procedure described for Objective 1. For each experimental unit, the total number of seeds that completed germination was expressed as a percentage of viable seeds, with total number of viable seeds equal to germinants plus viable as indicated by TZ test.

All data were analyzed using R version 4.4.1. Codes for executing statistical analyses are provided with the dataset.

Document Type

Dataset

Publication Date

2026

Publisher

New Mexico State University

Keywords

Beet curly top virus, integrated pest management, intrapopulation variation, Neoaliturus tenellus, osmotic potential, seedling emergence, weedy trait

Disciplines

Agriculture | Entomology | Plant Pathology | Weed Science

Department / Organizational Unit

Department of Entomology, Plant Pathology, and Weed Science

Copyright Statement

© Author(s), reuse allowed according to Creative Commons license

Variable Temperature and Moisture Requirements for Germination within Populations of Kochia (<i>Bassia scoparia</i>) in Field Margins

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